Method and device for executing communication via uplink access in wireless LAN system

ABSTRACT

The present specification relates to a method and a device for determination related to enhanced distributed channel access (EDCA). For example, it may be inappropriate for a STA to perform uplink communication based on EDCA. In this case, an AP and/or the STA can disable an EDCA function or operation. The present specification proposes various examples of a determination criterion and a determination method related to EDCA disabling.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2019/004811, filed on Apr. 22, 2019,which claims the benefit of earlier filing date and right of priority toKorean Application Nos. 10-2018-0045970, filed on Apr. 20, 2018,10-2018-0049839, filed on Apr. 30, 2018, and 10-2018-0049948, filed onApr. 30, 2018, and also claims the benefit of U.S. ProvisionalApplication No. 62/666,646, filed on May 3, 2018, the contents of whichare all hereby incorporated by reference herein in their entirety.

BACKGROUND Technical Field

The present specification relates to a technique for transmitting andreceiving data in wireless communication and, more particularly, to amethod and a device for performing communication through uplink accessin a wireless local area network (WLAN) system.

Related Art

A wireless local area network (WLAN) has been improved in various ways.For example, IEEE 802.11ax proposes an improved communicationenvironment using orthogonal frequency division multiple access (OFDMA)and downlink multi-user multiple-input multiple-output (DL MU MIMO)techniques.

This specification improves the existing IEEE 802.11ax standard orproposes technical features that can be used in a new communicationstandard. The new communication standard may be an extremely highthroughput (EHT) standard that is under discussion in recent times. TheEHT standard may employ a newly proposed increased bandwidth, animproved PPDU structure, an improved sequence, and a hybrid automaticrepeat request (HARQ) technique.

SUMMARY

The present specification proposes a technique for controlling uplinkcommunication in a wireless local area network (WLAN) system. In somecases, it may be difficult for a station (STA) to performcontention-based uplink communication. An example of contention-baseduplink communication may be uplink communication based on enhanceddistributed channel access (EDCA). For example, when the STA ispositioned at the edge of a basic service set (BSS), it may be difficultfor the STA to perform contention-based uplink transmission due to alack of transmission power.

To solve this problem, the present specification proposes an improvedmethod for controlling contention-based uplink communication.

An example of the present specification relates to a method and/or adevice for a wireless local area network (WLAN) system.

For example, a station (STA) may receive first control informationrelated to an enhanced distributed channel access (EDCA)-disablingoperation of the STA from an access point (AP). For example, the firstcontrol information may include at least one parameter related to anEDCA-disabling condition for the STA.

The STA may determine whether to disable an EDCA operation of the STAbased on the first control information. Determining to disable the EDCAoperation may be performed by the STA and may also be performed by theAP.

When necessary, the STA may transmit second control information relatedto the determination to the AP.

An example of the present specification provides an effect ofcontrolling contention-based uplink communication. For example, theexample of the present specification proposes a function ofdisabling/blocking contention-based uplink access. Accordingly, a STAperforms uplink communication according to an uplink multi-user (UL MU)scheme based on a trigger frame. As a result, the STA can normallyperform uplink communication even though having difficulty incontention-based access.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view illustrating the structure of a wirelesslocal area network (WLAN).

FIG. 2 illustrates a general link setup process.

FIG. 3 illustrates an example of a PPDU used in an IEEE standard.

FIG. 4 illustrates a layout of resource units (RUs) used in a band of 20MHz.

FIG. 5 illustrates a layout of RUs used in a band of 40 MHz.

FIG. 6 illustrates a layout of RUs used in a band of 80 MHz.

FIG. 7 illustrates another example of an HE PPDU.

FIG. 8 illustrates an example of a frame structure used in an IEEE802.11 system.

FIG. 9 illustrates an example of a trigger frame.

FIG. 10 illustrates an example of a common information field included ina trigger frame.

FIG. 11 illustrates an example of a subfield included in a per userinformation field.

FIG. 12 illustrates an EDCA-based channel access method in a WLANsystem.

FIG. 13 is a conceptual view illustrating a backoff procedure of EDCA.

FIG. 14 illustrates a frame transmission procedure in a WLAN system.

FIG. 15 illustrates an example of setting an NAV.

FIG. 16 is a procedure flowchart illustrating an example of anEDCA-disabling operation according to the present specification.

FIG. 17 illustrates an example of an OM control field.

FIG. 18 is a procedure flowchart illustrating another example of anEDCA-disabling operation according to the present specification.

FIG. 19 illustrates a method of performing UORA in a WLAN system.

FIG. 20 illustrates an example of additional information included in auser info field of a trigger frame.

FIG. 21 illustrates an example of control information according to anexample of the present specification.

FIG. 22 illustrates an operation according to a modified example of thepresent specification.

FIG. 23 illustrates an example of a PPDU to which an example of thepresent specification is applied.

FIG. 24 illustrates an example of a STA to which an example of thepresent specification is applied.

FIG. 25 is a block diagram specifically illustrating a transceiver.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

As used herein, a slash (/) or comma may indicate “and/or”. For example,“A/B” may indicate “A and/or B,” and therefore may mean “only A”, “onlyB”, or “A and B”. Technical features that are separately described inone drawing may be implemented separately or may be implementedsimultaneously.

As used herein, parentheses may indicate “for example”. Specifically,“control information (EHT-SIG)” may mean that “EHT-SIG” is proposed asan example of “control information”. Further, “control information(i.e., EHT-SIG)” may also mean that “EHT-SIG” is proposed as an exampleof “control information”.

The following examples of the present specification may be applied tovarious wireless communication systems. For example, the followingexamples of the present specification may be applied to a wireless localarea network (WLAN) system. For example, the present specification maybe applied to IEEE 802.11a/g/n/ac or IEEE 802.11ax. The presentspecification may also be applied to a newly proposed EHT standard orIEEE 802.11be.

Hereinafter, technical features of a WLAN system to which the presentspecification is applicable are described in order to describe technicalfeatures of the present specification.

FIG. 1 is a conceptual view illustrating the structure of a wirelesslocal area network (WLAN).

An upper part of FIG. 1 illustrates the structure of an infrastructurebasic service set (BSS) of institute of electrical and electronicengineers (IEEE) 802.11.

Referring the upper part of FIG. 1, the wireless LAN system may includeone or more infrastructure BSSs 100 and 105 (hereinafter, referred to asBSS). The BSSs 100 and 105 as a set of an AP and an STA such as anaccess point (AP) 125 and a station (STA1) 100-1 which are successfullysynchronized to communicate with each other are not concepts indicatinga specific region. The BSS 105 may include one or more STAs 105-1 and105-2 which may be joined to one AP 130.

The BSS may include at least one STA, APs providing a distributionservice, and a distribution system (DS) 110 connecting multiple APs.

The distribution system 110 may implement an extended service set (ESS)140 extended by connecting the multiple BSSs 100 and 105. The ESS 140may be used as a term indicating one network configured by connectingone or more APs 125 or 230 through the distribution system 110. The APincluded in one ESS 140 may have the same service set identification(SSID).

A portal 120 may serve as a bridge which connects the wireless LANnetwork (IEEE 802.11) and another network (e.g., 802.X).

In the BSS illustrated in the upper part of FIG. 1, a network betweenthe APs 125 and 130 and a network between the APs 125 and 130 and theSTAs 100-1, 105-1, and 105-2 may be implemented. However, the network isconfigured even between the STAs without the APs 125 and 130 to performcommunication. A network in which the communication is performed byconfiguring the network even between the STAs without the APs 125 and130 is defined as an Ad-Hoc network or an independent basic service set(IBSS).

A lower part of FIG. 1 illustrates a conceptual view illustrating theIBSS.

Referring to the lower part of FIG. 1, the IBSS is a BSS that operatesin an Ad-Hoc mode. Since the IBSS does not include the access point(AP), a centralized management entity that performs a managementfunction at the center does not exist. That is, in the IBSS, STAs 150-1,150-2, 150-3, 155-4, and 155-5 are managed by a distributed manner. Inthe IBSS, all STAs 150-1, 150-2, 150-3, 155-4, and 155-5 may beconstituted by movable STAs and are not permitted to access the DS toconstitute a self-contained network.

The STA as a predetermined functional medium that includes a mediumaccess control (MAC) that follows a regulation of an Institute ofElectrical and Electronics Engineers (IEEE) 802.11 standard and aphysical layer interface for a radio medium may be used as a meaningincluding all of the APs and the non-AP stations (STAs).

The STA may be called various a name such as a mobile terminal, awireless device, a wireless transmit/receive unit (WTRU), user equipment(UE), a mobile station (MS), a mobile subscriber unit, or just a user.

FIG. 2 illustrates a general link setup process.

In S210, a STA may perform a network discovery operation. The networkdiscovery operation may include a scanning operation of the STA. Thatis, to access a network, the STA needs to discover a participatingnetwork. The STA needs to identify a compatible network beforeparticipating in a wireless network, and a process of identifying anetwork present in a particular area is referred to as scanning.Scanning methods include active scanning and passive scanning.

FIG. 2 illustrates a network discovery operation including an activescanning process. In active scanning, a STA performing scanningtransmits a probe request frame and waits for a response to the proberequest frame in order to identify which AP is present around whilemoving to channels. A responder transmits a probe response frame as aresponse to the probe request frame to the STA having transmitted theprobe request frame. Here, the responder may be a STA that transmits thelast beacon frame in a BSS of a channel being scanned. In the BSS, sincean AP transmits a beacon frame, the AP is the responder. In an IBSS,since STAs in the IBSS transmit a beacon frame in turns, the responderis not fixed. For example, when the STA transmits a probe request framevia channel 1 and receives a probe response frame via channel 1, the STAmay store BSS-related information included in the received proberesponse frame, may move to the next channel (e.g., channel 2), and mayperform scanning (e.g., transmits a probe request and receives a proberesponse via channel 2) by the same method.

Although not shown in FIG. 2, scanning may be performed by a passivescanning method. In passive scanning, a STA performing scanning may waitfor a beacon frame while moving to channels. A beacon frame is one ofmanagement frames in IEEE 802.11 and is periodically transmitted toindicate the presence of a wireless network and to enable the STAperforming scanning to find the wireless network and to participate inthe wireless network. In a BSS, an AP serves to periodically transmit abeacon frame. In an IBSS, STAs in the IBSS transmit a beacon frame inturns. Upon receiving the beacon frame, the STA performing scanningstores information about a BSS included in the beacon frame and recordsbeacon frame information in each channel while moving to anotherchannel. The STA having received the beacon frame may store BSS-relatedinformation included in the received beacon frame, may move to the nextchannel, and may perform scanning in the next channel by the samemethod.

After discovering the network, the STA may perform an authenticationprocess in S220. The authentication process may be referred to as afirst authentication process to be clearly distinguished from thefollowing security setup operation in S240. The authentication processin S220 may include a process in which the STA transmits anauthentication request frame to the AP and the AP transmits anauthentication response frame to the STA in response. The authenticationframes used for an authentication request/response are managementframes.

The authentication frames may include information about anauthentication algorithm number, an authentication transaction sequencenumber, a status code, a challenge text, a robust security network(RSN), and a finite cyclic group.

The STA may transmit the authentication request frame to the AP. The APmay determine whether to allow the authentication of the STA based onthe information included in the received authentication request frame.The AP may provide the authentication processing result to the STA viathe authentication response frame.

When the STA is successfully authenticated, the STA may perform anassociation process in S230. The association process includes a processin which the STA transmits an association request frame to the AP andthe AP transmits an association response frame to the STA in response.The association request frame may include, for example, informationabout various capabilities, a beacon listen interval, a service setidentifier (SSID), a supported rate, a supported channel, RSN, amobility domain, a supported operating class, a traffic indication map(TIM) broadcast request, and an interworking service capability. Theassociation response frame may include, for example, information aboutvarious capabilities, a status code, an association ID (AID), asupported rate, an enhanced distributed channel access (EDCA) parameterset, a received channel power indicator (RCPI), a receivedsignal-to-noise indicator (RSNI), a mobility domain, a timeout interval(association comeback time), an overlapping BSS scanning parameter, aTIM broadcast response, and a QoS map.

In S240, the STA may perform a security setup process. The securitysetup process in S240 may include a process of setting up a private keythrough four-way handshaking, for example, through an extensibleauthentication protocol over LAN (EAPOL) frame.

FIG. 3 illustrates an example of a PPDU used in an IEEE standard.

As illustrated in FIG. 3, various types of PHY protocol data units(PPDUs) are used in IEEE a/g/n/ac standards. Specifically, a LTF and aSTF include a training signal, a SIG-A and a SIG-B include controlinformation for a receiving STA, and a data field includes user datacorresponding to a PSDU (MAC PDU/aggregated MAC PDU).

FIG. 3 also includes an example of an HE PPDU according to IEEE802.11ax. The HE PPDU according to FIG. 3 is an illustrative PPDU formultiple users. An HE-SIG-B may be included only in a PPDU for multipleusers, and an HE-SIG-B may be omitted in a PPDU for a single user.

As illustrated in FIG. 3, the HE-PPDU for multiple users (MUs) mayinclude a legacy-short training field (L-STF), a legacy-long trainingfield (L-LTF), a legacy-signal (L-SIG), a high efficiency-signal A(HE-SIG A), a high efficiency-signal-B (HE-SIG B), a highefficiency-short training field (HE-STF), a high efficiency-longtraining field (HE-LTF), a data field (alternatively, an MAC payload),and a packet extension (PE) field. The respective fields may betransmitted for illustrated time periods (i.e., 4 or 8 μs).

Hereinafter, a resource unit (RU) used for a PPDU is described. An RUmay include a plurality of subcarriers (or tones). An RU may be used totransmit a signal to a plurality of STAs according to OFDMA. Further, anRU may also be defined to transmit a signal to one STA. An RU may beused for an STF, an LTF, a data field, or the like.

FIG. 4 illustrates a layout of resource units (RUs) used in a band of 20MHz.

As illustrated in FIG. 4, resource units (RUs) corresponding todifferent numbers of tones (i.e., subcarriers) may be used to form somefields of an HE-PPDU. For example, resources may be allocated inillustrated RUs for an HE-STF, an HE-LTF, and a data field.

As illustrated in the uppermost part of FIG. 4, a 26-unit (i.e., a unitcorresponding to 26 tones) may be disposed. Six tones may be used for aguard band in the leftmost band of the 20 MHz band, and five tones maybe used for a guard band in the rightmost band of the 20 MHz band.Further, seven DC tones may be inserted in a center band, that is, a DCband, and a 26-unit corresponding to 13 tones on each of the left andright sides of the DC band may be disposed. A 26-unit, a 52-unit, and a106-unit may be allocated to other bands. Each unit may be allocated fora receiving STA, that is, a user.

The layout of the RUs in FIG. 4 may be used not only for a multipleusers (MUs) but also for a single user (SU), in which case one 242-unitmay be used and three DC tones may be inserted as illustrated in thelowermost part of FIG. 4.

Although FIG. 4 proposes RUs having various sizes, that is, a 26-RU, a52-RU, a 106-RU, and a 242-RU, specific sizes of RUs may be extended orincreased. Therefore, the present embodiment is not limited to thespecific size of each RU (i.e., the number of corresponding tones).

FIG. 5 illustrates a layout of RUs used in a band of 40 MHz.

Similarly to FIG. 4 in which RUs having various sizes are used, a 26-RU,a 52-RU, a 106-RU, a 242-RU, a 484-RU, and the like may be used in anexample of FIG. 5. Further, five DC tones may be inserted in a centerfrequency, 12 tones may be used for a guard band in the leftmost band ofthe 40 MHz band, and 11 tones may be used for a guard band in therightmost band of the 40 MHz band.

As illustrated in FIG. 5, when the layout of the RUs is used for asingle user, a 484-RU may be used. The specific number of RUs may bechanged similarly to FIG. 4.

FIG. 6 illustrates a layout of RUs used in a band of 80 MHz.

Similarly to FIG. 4 and FIG. 5 in which RUs having various sizes areused, a 26-RU, a 52-RU, a 106-RU, a 242-RU, a 484-RU, a 996-RU, and thelike may be used in an example of FIG. 6. Further, seven DC tones may beinserted in the center frequency, 12 tones may be used for a guard bandin the leftmost band of the 80 MHz band, and 11 tones may be used for aguard band in the rightmost band of the 80 MHz band. In addition, a26-RU corresponding to 13 tones on each of the left and right sides ofthe DC band may be used.

As illustrated in FIG. 6, when the layout of the RUs is used for asingle user, a 996-RU may be used, in which case five DC tones may beinserted.

The specific number of RUs may be changed similarly to FIG. 4 and FIG.5.

FIG. 7 illustrates another example of an HE PPDU.

Technical characteristics of the HE PPDU illustrated in FIG. 7 may alsobe applied to an EHT PPDU to be newly proposed. For example, technicalcharacteristics applied to an HE-SIG may also be applied to an EHT-SIG,and technical characteristics of an HE-STF/LTF may also be applied to anEHT-SFT/LTF.

An L-STF 700 may include a short training orthogonal frequency divisionmultiplexing (OFDM) symbol. The L-STF 700 may be used for framedetection, automatic gain control (AGC), diversity detection, and coarsefrequency/time synchronization.

An L-LTF 710 may include a long training orthogonal frequency divisionmultiplexing (OFDM) symbol. The L-LTF 710 may be used for finefrequency/time synchronization and channel prediction.

An L-SIG 720 may be used for transmitting control information. The L-SIG720 may include information about a data rate and a data length.Further, the L-SIG 720 may be repeatedly transmitted. That is, a formatin which the L-SIG 720 is repeated (which may be referred to, forexample, as an R-LSIG) may be configured.

An HE-SIG-A 730 may include control information common to a receivingSTA.

Specifically, the HE-SIG-A 730 may include information about 1) a DL/ULindicator, 2) a BSS color field indicating an identify of a BSS, 3) afield indicating a remaining time of a current TXOP period, 4) abandwidth field indicating at least one of 20, 40, 80, 160 and 80+80MHz, 5) a field indicating an MCS technique applied to an HE-SIG-B, 6)an indication field regarding whether the HE-SIG-B is modulated by adual subcarrier modulation technique for MCS, 7) a field indicating thenumber of symbols used for the HE-SIG-B, 8) a field indicating whetherthe HE-SIG-B is configured for a full bandwidth MIMO transmission, 9) afield indicating the number of symbols of the HE-LTF, 10) a fieldindicating the length of the HE-LTF and a CP length, 11) a fieldindicating whether an OFDM symbol is present for LDPC coding, 12) afield indicating control information regarding packet extension (PE),13) a field indicating information on a CRC field of the HE-SIG-A, andthe like. A specific field of the HE-SIG-A may be added or partiallyomitted. Further, some fields of the HE-SIG-A may be partially added oromitted in other environments other than a multi-user (MU) environment

An HE-SIG-B 740 may be included only in the case of the PPDU for themultiple users (MUs) as described above. Basically, an HE-SIG-A 750 oran HE-SIG-B 760 may include resource allocation information (or virtualresource allocation information) for at least one receiving STA.

An HE-STF 750 may be used for improving automatic gain controlestimation in a multiple input multiple output (MIMO) environment or anOFDMA environment.

An HE-LTF 760 may be used for estimating a channel in the MIMOenvironment or the OFDMA environment.

The size of fast Fourier transform (FFT)/inverse fast Fourier transform(IFFT) applied to the HE-STF 750 and a field after the HE-STF 750 may bedifferent from the size of FFT/IFFT applied to a field before the HE-STF750. For example, the size of the FFT/IFFT applied to the HE-STF 750 andthe field after the HE-STF 750 may be four times larger than the size ofthe FFT/IFFT applied to the field before the HE-STF 750.

For example, when at least one field of the L-STF 700, the L-LTF 710,the L-SIG 720, the HE-SIG-A 730, and the HE-SIG-B 740 on the PPDU ofFIG. 7 is referred to as a first field, at least one of the data field770, the HE-STF 750, and the HE-LTF 760 may be referred to as a secondfield. The first field may include a field related to a legacy system,and the second field may include a field related to an HE system. Inthis case, the fast Fourier transform (FFT) size and the inverse fastFourier transform (IFFT) size may be defined as a size which is N (N isa natural number, for example, N=1, 2, or 4) times larger than theFFT/IFFT size used in the legacy wireless LAN system. That is, theFFT/IFFT having the size may be applied, which is N (=4) times largerthan the first field of the HE PPDU. For example, 256 FFT/IFFT may beapplied to a bandwidth of 20 MHz, 512 FFT/IFFT may be applied to abandwidth of 40 MHz, 1024 FFT/IFFT may be applied to a bandwidth of 80MHz, and 2048 FFT/IFFT may be applied to a bandwidth of continuous 160MHz or discontinuous 160 MHz.

In other words, a subcarrier space/subcarrier spacing may have a sizewhich is 1/N times (N is the natural number, e.g., N=4, the subcarrierspacing is set to 78.125 kHz) the subcarrier space used in the legacywireless LAN system. That is, subcarrier spacing having a size of 312.5kHz, which is legacy subcarrier spacing may be applied to the firstfield of the HE PPDU and a subcarrier space having a size of 78.125 kHzmay be applied to the second field of the HE PPDU.

Alternatively, an IDFT/DFT period applied to each symbol of the firstfield may be expressed to be N (=4) times shorter than the IDFT/DFTperiod applied to each data symbol of the second field. That is, theIDFT/DFT length applied to each symbol of the first field of the HE PPDUmay be expressed as 3.2 μs and the IDFT/DFT length applied to eachsymbol of the second field of the HE PPDU may be expressed as 3.2 μs*4(=12.8 μs). The length of the OFDM symbol may be a value acquired byadding the length of a guard interval (GI) to the IDFT/DFT length. Thelength of the GI may have various values, such as 0.4 μs, 0.8 μs, 1.6μs, 2.4 μs, and 3.2 μs.

For convenience of description, FIG. 7 shows that a frequency band usedfor the first field and a frequency band used for the second fieldaccurately correspond to each other, but both frequency bands may notcompletely correspond to each other in actual. For example, a primaryband of the first field (L-STF, L-LTF, L-SIG, HE-SIG-A, and HE-SIG-B)corresponding to the first frequency band may be the same as a primaryband of the second field (HE-STF, HE-LTF, and Data), but boundaries ofthe respective frequency bands may not correspond to each other. Asillustrated in FIG. 4 to FIG. 6, since a plurality of null subcarriers,DC tones, guard tones, and the like are inserted when arranging RUs, itmay be difficult to accurately adjust the boundaries.

A user, that is, a receiving STA, may receive the HE-SIG-A 730 and maybe instructed to receive a downlink PPDU based on the HE-SIG-A 730. Inthis case, the STA may perform decoding based on the FFT size changedfrom the HE-STF 750 and the field after the HE-STF 750. On the contrary,when the STA may not be instructed to receive a downlink PPDU based onthe HE-SIG-A 730, the STA may stop decoding and may configure a networkallocation vector (NAV). A cyclic prefix (CP) of the HE-STF 750 may havea larger size than a CP of another field, and the STA may decode adownlink PPDU by changing the FFT size in a period of the CP.

Hereinafter, in an embodiment, data (or a frame) transmitted from an APto an STA may be referred to as downlink data (or a downlink frame), anddata (a frame) transmitted from an STA to an AP may be referred to asuplink data (an uplink frame). Further, transmission from an AP to anSTA may be referred to as downlink transmission, and transmission froman STA to an AP may be referred to as uplink transmission.

FIG. 8 illustrates an example of a frame structure used in an IEEE802.11 system. An STF, an LTF, and a SIG field illustrated in FIG. 8 maybe the same as or equivalent to the (HT/VHT/EHT)-STF, the LTF, and theSIG field illustrated in FIG. 3 or FIG. 7. Further, a data fieldillustrated in FIG. 8 may be the same as or equivalent to a data fieldillustrated in FIG. 3 or FIG. 7.

The data field may include a service field, a physical layer servicedata unit (PSDU), and a PPDU tail bit, and may optionally include apadding bit. Some bits of the service field may be used forsynchronization of a descrambler at a receiving end. The PSDU maycorrespond to a MAC protocol data unit (MPDU) defined in a MAC layer andmay include data generated/used in a higher layer. The PPDU tail bit maybe used to return an encoder to a zero state. The padding bit may beused to adjust the length of the data field in a specific unit.

The MPDU is defined according to various MAC frame formats, and a basicMAC frame includes a MAC header, a frame body, and a frame checksequence (FCS). The MAC frame may include an MPDU and may betransmitted/received through a PSDU of a data part of a PPDU frameformat.

The MAC header includes a frame control field, a duration/ID field, anaddress field, or the like. The frame control field may include controlinformation required for frame transmission/reception. The duration/IDfield may be set to a time for transmitting a corresponding frame or thelike.

The duration/ID field included in the MAC header may be set to a 16-bitlength (e.g., B0˜B15). Content included in the duration/ID field mayvary depending on a frame type and a subtype, whether it is transmittedduring a contention free period (CFP), QoS capability of a transmittingSTA, or the like. In a control frame of which a subtype is PS-poll, theduration/ID field may include an AID of a transmitting STA (e.g.,through 14 LSBs), and two MSBs may be set to 1. (ii) In framestransmitted by a point coordinator (PC) or a non-QoS STA during a CFP,the duration/ID field may be set to a fixed value (e.g., 32768). (iii)In other frames transmitted by the non-QoS STA or control framestransmitted by the QoS STA, the duration/ID field may include a durationvalue defined for each frame type. In a data frame or management frametransmitted by the QoS STA, the duration/ID field may include a durationvalue defined for each frame type. For example, if the duration/ID fieldis set to B15=0, the duration/ID field is used to indicate a TXOPduration, and B0 to B14 may be used to indicate an actual TXOP duration.The actual TXOP duration indicated by B0 to B14 may be any one of 0 to32767, and a unit thereof may be a microsecond (us). However, if theduration/ID field indicates a fixed TXOP duration value (e.g., 32768),B15=1 and B0 to B14=0. If set to B14=1 and B15=1, the duration/ID fieldis used to indicate an AID, and B0 to B13 indicate one AID ranging from1 to 2007.

A frame control field of the MAC header may include Protocol Version,Type, Subtype, To DS, From DS, More Fragment, Retry, Power Management,More Data, Protected Frame, and Order subfields.

Hereinafter, multi-user (MU) transmission applied to this specificationis described. A method and a device according to this specificationsupport MU transmission. For example, for DL data, an orthogonalfrequency-division multiple access (OFDMA) scheme and a multi-usermultiple-input multiple-output (MU MIMO) scheme may be used, and acombination of the OFDMA scheme and the MU MIMO scheme may also be used.That is, a transmitting STA according to the present specification mayallocate different RUs to a plurality of users (i.e., OFDMA) or mayallocate different spatial streams on the same UR (i.e., MU-MIMO).Further, the transmitting STA may simultaneously use the OFDMA schemeand the MU MIMO scheme within one PPDU.

The transmitting STA according to the present specification may performUL-MU communication using a trigger frame. Specific features of thetrigger frame are described with reference to FIG. 9 to FIG. 11.

To trigger UL-MU communication, the transmitting STA (i.e., an AP) mayobtain a TXOP to transmit a trigger frame via contention for accessing amedium. When the trigger frame is completely transmitted, a plurality ofreceiving STAs participating in the UL-MU communication simultaneouslytransmits a trigger-based (TB) PPDU after a certain time (e.g., SIFS).Basic technical features applied to the TB-PPDU are described in FIG. 3and FIG. 7.

When UL-MU communication is used, the OFDMA scheme or the MU MIMO schememay also be used, or the OFDMA scheme and the MU MIMO scheme may be usedsimultaneously.

FIG. 9 illustrates an example of a trigger frame. The trigger frameillustrated in FIG. 9 allocates resources for uplink multiple-user (MU)transmission and may be transmitted from an AP. The trigger frame may beconfigured as a MAC frame and may be included in a PPDU. For example,the trigger frame may be transmitted through the PPDU illustrated inFIG. 3. If the trigger frame is transmitted through the PPDU of FIG. 3,the trigger frame may be included in the illustrated data field.

Some fields illustrated in FIG. 9 may be omitted, and other fields maybe added. The length of each illustrated field may be varied.

A frame control field 910 shown in FIG. 9 may include information abouta version of a MAC protocol and other additional control information,and a duration field 920 may include time information for NAV setting orinformation about an identifier (e.g., AID) of a STA.

An RA field 930 may include address information about a receiving STA ofthe trigger frame and may be optionally omitted. A TA field 940 includesaddress information about an STA (e.g., AP) for transmitting the triggerframe, and a common information field 950 includes common controlinformation applied to the receiving STA for receiving the triggerframe. For example, a field indicating the length of an L-SIG field ofan uplink PPDU transmitted in response to the trigger frame orinformation controlling the content of a SIG-A field (i.e., an HE-SIG-Afield) of the uplink PPDU transmitted in response to the trigger framemay be included. Further, as the common control information, informationabout the length of a CP of the uplink PPDU transmitted in response tothe trigger frame or information about the length of an LTF thereof maybe included.

The trigger frame of FIG. 9 preferably includes per user informationfields 960 #1 to 960 #N corresponding to the number of receiving STAsreceiving the trigger frame of FIG. 9. A per user information field mayalso be referred to as an allocation field.

Further, the trigger frame of FIG. 9 may include a padding field 970 anda sequence field 980.

Each of the per user information fields 960 #1 to 960 #N illustrated inFIG. 9 preferably includes a plurality of subfields.

FIG. 10 illustrates an example of a common information field included ina trigger frame. Some subfields illustrated in FIG. 10 may be omitted,and other subfields may be added. The length of each illustratedsubfield may be varied.

A length field 1010 has that same value as a length field of an L-SIGfield of an uplink PPDU, which is transmitted in response to the triggerframe, and the length field of the L-SIG field of the uplink PPDUindicates the length of the uplink PPDU. As a result, the length field1010 of the trigger frame may be used to indicate the length of thecorresponding uplink PPDU.

A cascade indicator field 1020 indicates whether a cascade operation isperformed. A cascade operation means that both downlink MU transmissionand uplink MU transmission are performed within the same TXOP, that is,downlink MU transmission is performed, and then uplink MU transmissionis performed after a preset period of time (e.g., SIFS). In the cascadeoperation, only one transmission device performing downlinkcommunication (e.g., AP) may exist, and a plurality of transmissiondevices performing uplink communication (e.g., non-AP) may exist.

A CS request field 1030 indicates whether the status or NAV of awireless medium is required to be considered in a situation where areception device receiving the trigger frame transmits a correspondinguplink PPDU.

An HE-SIG-A information field 1040 may include information controllingthe content of a SIG-A field (i.e., HE-SIG-A field) of the uplink PPDUtransmitted in response to the trigger frame.

A CP and LTF type field 1050 may include information about an LTF lengthand a CP length of the uplink PPDU transmitted in response to thetrigger frame. A trigger type field 1060 may indicate a purpose of thetrigger frame, for example, general triggering, triggering forbeamforming, a request for a block ACK/NACK, or the like.

In the present specification, it may be assumed that the trigger typefield 1060 of the trigger frame indicates a trigger frame of a basictype for general triggering. For example, a trigger frame of a basictype may be referred to as a basic trigger frame.

FIG. 11 illustrates an example of a subfield included in a per userinformation field. The per user information field 1100 in FIG. 11 may beunderstood as one of the per user information fields 960 #1 to 960 #Nillustrated above in FIG. 9. Some subfields included in the per userinformation field 1100 in FIG. 11 may be omitted, and other subfieldsmay be added. The length of each illustrated subfield may be varied.

A user identifier field 1110 indicates an identifier of an STA (i.e., areceiving STA) which corresponds to the per user information, and anexample of the identifier may be the entirety or part of an associationidentifier (AID) of the receiving STA.

A RU allocation field 1120 may be included in the per user informationfield. Specifically, when the receiving STA, which is identified by theuser identifier field 1110, transmits an uplink PPDU in response to thetrigger frame of FIG. 9, the STA transmits the uplink PPDU via an RUindicated by the RU allocation field 1120. In this case, it ispreferable that the RU indicated by the RU allocation field 1120corresponds to the RU illustrated in FIG. 4, FIG. 5, or FIG. 6.

A subfield of FIG. 11 may include a coding type field 1130. The codingtype field 1130 may indicate the coding type of the uplink PPDUtransmitted in response to the trigger frame of FIG. 9. For example,when BBC coding is applied to the uplink PPDU, the coding type field1130 may be set to 1. When LDPC coding is applied to the uplink PPDU,the coding type field 1130 may be set to 0.

A subfield of FIG. 11 may include a coding type field 1130. The codingtype field 1130 may indicate the coding type of the uplink PPDUtransmitted in response to the trigger frame of FIG. 9. For example,when BBC coding is applied to the uplink PPDU, the coding type field1130 may be set to 1. When LDPC coding is applied to the uplink PPDU,the coding type field 1130 may be set to 0.

In the present specification, a basic trigger frame may be understood asa variant of a trigger frame. A basic trigger frame may further includea trigger-dependent user info field 1150 in the per user informationfields 960 #1 to 960 #N.

Hereinafter, an enhanced distributed channel access (EDCA) scheme, thatis, an EDCA-based channel access method, is described.

FIG. 12 illustrates an EDCA-based channel access method in a WLANsystem. In a WLAN system, an STA (or AP) may perform channel accessaccording to a plurality of user priority levels defined for EDCA.

Specifically, in order to transmit a quality of service (QoS) data framebased on a plurality of user priority levels, four access categories(ACs, e.g., background (AC_BK), best effort (AC_BE), video (AC_VI), andvoice (AC_VO)) may be defined.

The STA may receive traffic data (e.g., a MAC service data unit (MSDU))having a preset user priority level from a higher layer (e.g., a logicallink control (LLC) layer).

For example, in order to determine the transmission order of MAC framesto be transmitted by the STA, a differential value may be set for eachset of traffic data in a user priority level. In this specification, auser priority level may be understood as a traffic identifier(hereinafter, “TID”) indicating a characteristics of traffic data. Forexample, TID 1, 2, 0, 3, 4, 5, 6, and 7 may be mapped to AC_BK, AC_BK,AC_BE, AC_BE, AC_VI, AC_VI, AC_VO, and AC_VO, respectively.

That is, traffic data having a user priority level (i.e., TID) of 1 or 2may be buffered in a transmission queue 1250 of an AC_BK type. Trafficdata having a user priority level (i.e., TID) of 0 or 3 may be bufferedin a transmission queue 1240 of an AC_BE type. Traffic data having auser priority level (i.e., TID) of 4 or 5 may be buffered in atransmission queue 1230 of an AC_VI type. Traffic data having a userpriority level (i.e., TID) of 6 or 7 may be buffered in a transmissionqueue 1220 of an AC_VO type.

Instead of DCF interframe space (DIFS), CWmin, and CWmax, which areparameters for a backoff procedure based on a legacy distributedcoordination function (DCF), a set (or group) of EDCA parameters, whichare arbitration interframe space (AIFS)[AC], CWmin[AC], CWmax[AC], andTXOP limit[AC], may be used for a backoff procedure of a STA performingEDCA.

There may be a difference in transmission priority levels between ACsbased on a set of differential EDCA parameters. The default values ofthe set of EDCA parameters (i.e., AIFS[AC], CWmin[AC], CWmax[AC], andTXOP limit[AC]) corresponding to each AC may be fixedly determinedaccording to a WLAN standard.

For example, CWmin[AC], CWmax[AC], AIFS[AC], and TXOP limit[AC] forAC_BK may be determined to be 31, 1023, 7, and 0 ms. CWmin[AC],CWmax[AC], AIFS[AC], and TXOP limit[AC] for AC_BE may be determined tobe 31, 1023, 3, and 0 ms, respectively. CWmin[AC], CWmax[AC], AIFS[AC],and TXOP limit[AC] for AC_VI may be determined to be 15, 31, 2, and3.008 ms, respectively. CWmin[AC], CWmax[AC], AIFS[AC], and TXOPlimit[AC] for AC_VO may be determined to be 7, 15, 2, and 1.504 ms,respectively. These specific values may be changed.

The set of EDCA parameters for each AC may be configured to have defaultvalues or may be loaded in a beacon frame to be transmitted from an APto each STA. As AIFS[AC] and CWmin[AC] have smaller values, AIFS[AC] andCWmin[AC] have higher priority levels, thus having a shorter delay inchannel access delay and using a larger number of bands in a giventraffic environment.

The set of EDCA parameters may include information about channel accessparameters (e.g., AIFS [AC], CWmin[AC], and CWmax[AC]) for each AC.

A backoff procedure for EDCA may be performed based on a set of EDCAparameters individually configured for four ACs included in each STA. Anadequate configuration of EDCA parameter values defining differentchannel access parameters for each AC may optimize network performanceand may also increase the transmission effect by the priority level oftraffic.

Therefore, in order to ensure or fair media access for all STAsparticipating in the network, the AP of the WLAN system needs to performoverall management and coordination functions for the EDCA parameters.

Referring to FIG. 12, one STA (or AP) 1200 may include a virtual mapper1210, a plurality of transmission queues 1220 to 1250, and a virtualcollision handler 1260. The virtual mapper 1210 of FIG. 12 may serve tomap an MSDU received from a logical link control (LLC) layer to atransmission queue corresponding to each AC.

The plurality of transmission queues 1220 to 1250 may serve asindividual EDCA contention entities for wireless media access within oneSTA (or AP). For example, the transmission queue 1220 of the AC_VO typeof FIG. 12 may include one frame 1221 for a second STA (not shown).

The transmission queue 1230 of the AC_VI type may include three frames1231 to 1233 for a first STA (not shown) and one frame 1234 for a thirdSTA according to the order in which the frames are to be transmitted toa physical layer.

The transmission queue 1240 of the AC_BE type of FIG. 12 may include oneframe 1241 for a second STA (not shown), one frame 1242 for a third STA(not shown), and one frame 1243 for a second STA (not shown) accordingto the order in which the frames are to be transmitted to the physicallayer.

The transmission queue 1250 of the AC_BK type of FIG. 12 may not includea frame to be transmitted to the physical layer.

For example, the frame 1221 included in the transmission queue 1220 ofthe AC_VO type of FIG. 12 may be understood as one MAC Protocol DataUnit (MPDU) concatenated with a plurality of traffic data (i.e., MSDUs)received from a higher layer (i.e., the LLC layer).

Also, the frame 1221 included in the transmission queue 1220 of theAC_VO type of FIG. 12 may be understood as one MPDU concatenated with aplurality of traffic data (i.e., MSDUs) having a traffic identifier(TID) of either 6 or 7.

The frame 1231 included in the transmission queue 1230 of the AC_VI typeof FIG. 12 may be interpreted and understood as one MAC Protocol DataUnit (MPDU) that is concatenated with a plurality of traffic data (i.e.,MSDUs), which are received from a higher layer (i.e., LLC layer).

The frame 1231 included in the transmission queue 1230 of the AC_VI typeof FIG. 12 may be understood as one MPDU concatenated with a pluralityof traffic data (i.e., MSDUs) having a traffic identifier (TID) ofeither 4 or 5.

Similarly, each of the other frames 1232, 1233, and 1234 included in thetransmission queue 1230 of the AC_VI type may be understood as one MPDUconcatenated with a plurality of traffic data (i.e., MSDUs) having atraffic identifier (TID) of either 4 or 5.

The frame 1241 included in the transmission queue 1240 of the AC_BE typemay be understood as one MPDU concatenated with a plurality of trafficdata (i.e., MSDUs) having a traffic identifier (TID) of either 0 or 3.

Similarly, each of the other frames 1242 and 1243 included in thetransmission queue 1240 of the AC_BE type may be understood as one MPDUconcatenated with a plurality of traffic data (i.e., MSDUs) having atraffic identifier (TID) of any either 0 or 3.

Each of the frames 1221, 1231 to 1234, and 1241 to 1243 may beunderstood as a frame that does not exceed a predetermined traffic size.

When there are one or more ACs for which the backoff procedure has beencompleted at the same time, a collision between the ACs may becoordinated according to an EDCA function (EFCAF) included in thevirtual collision handler 1260.

Specifically, a frame included in an AC having a higher priority levelamong colliding ACs may be transmitted first, thereby resolving acollision in a STA. In this case, other ACs may increase a contentionwindow and may then update a backoff count using a backoff valuereselected based on the increased contention window.

A transmission opportunity (TXOP) may be started when a channel isaccessed in accordance with an EDCA rule. When two or more frames areaccumulated in one AC, and if an EPCA TXOP is acquired, the AC of anEDCA MAC layer may attempt to transmit a plurality of frames. When theSTA has already transmitted one frame, and if the STA can transmit anext frame in the same AC and can receive the ACK of the next framewithin the remaining TXOP time, the STA may attempt to transmit the nextframe after a time interval of SIFS.

A TXOP limit value may be set as a default value in the AP and the STA,or a frame related to the TXOP limit value may be transmitted to the STAfrom the AP.

When the size of a data frame to be transmitted exceeds the TXOP limitvalue, the AP may fragment the frame into a plurality of smaller frames.Subsequently, the fragmented frames may be transmitted within a rangethat does not exceed the TXOP limit value.

FIG. 13 is a conceptual view illustrating a backoff procedure of EDCA.

A plurality of STAs may share a wireless medium based on a distributedcoordination function (hereinafter, “DCF”). In order to control acollision between STAs, the DCF may use carrier sense multipleaccess/collision avoidance (hereinafter, “CSMA/CA”) as an accessprotocol.

In a channel access method using the DCF, if a medium is not occupiedduring one DCF inter frame space (DIFS) (i.e., if a channel is idle), aSTA may transmit an MPDU internally determined.

When it is determined by a carrier sensing mechanism that the wirelessmedium is used by another STA (i.e., that the channel is busy), the STAmay determine the size of a contention window (hereinafter, “CW”) andmay then perform a backoff procedure.

In order to perform the backoff procedure, each STA may configure abackoff value, which is arbitrarily selected within the contentionwindow (CW), in a backoff counter. In this specification, a timerepresenting a backoff value, which is selected by each STA, in slottimes may be understood as the backoff window illustrated in FIG. 13.

Each STA may perform a backoff procedure for channel access by countingdown a backoff window in slot times. Among the plurality of STAs, an STAselecting the relatively shortest backoff window may obtain atransmission opportunity (hereinafter, “TXOP”) as the right to occupy amedium.

During a time period for the TXOP, the remaining STAs may suspend thecountdown operation. The remaining STAs may wait until the time periodfor the TXOP expires. After the time period for the TXOP expires, theremaining STAs may resume the suspended countdown operation in order tooccupy the wireless medium.

According to the transmission method based on the DCF, it is possible toprevent a collision which may occur when a plurality of STAssimultaneously transmits a frame. However, the channel access methodusing the DCF does not have the concept of a transmission priority level(i.e., a user priority level). That is, using the DCF cannot guaranteethe quality of service (QoS) of traffic to be transmitted by a STA.

In order to resolve this problem, a hybrid coordination function(hereinafter, “HCF”) as a new coordination function is defined in802.11e. The newly defined HCF has more enhanced performance than thechannel access performance of the legacy DCF. For enhancing QoS, the HCFmay employ two different types of channel access methods, which areHCF-controlled channel access (HCCA) of a polling method andcontention-based enhanced distributed channel access (EDCA).

Referring to FIG. 13, the STA assumes that EDCA is performed for thetransmission of traffic data buffered in the STA. Referring to Table 1,user priority levels configured for individual traffic data may bedifferentiated to eight levels.

Each STA may include four types (AC_BK, AC_BE, AC_VI, and AC_VO) ofoutput queues mapped to eight user priority levels in Table 1.

The STA according to this embodiment may transmit traffic data based onan arbitration interframe space (AIFS) corresponding to a user prioritylevel instead of a DCF interframe space (DIFS) conventionally used.

To facilitate the understanding of this specification, interframespacing mentioned in 802.11 is be described. For example, interframespacing (IFS) may correspond to a reduced interframe space (RIFS), ashort interframe space (SIFS), a PCF interframe space (PIFS), a DCFinterframe space (DIFS), an arbitration interframe space (AIFS), or anextended interframe space (EIFS).

The interframe spacing (IFS) may be determined depending on attributesspecified by the physical layer of the STA regardless of the bit rate ofthe STA. Among the IFSs, IFSs other than the AIFS may be understood as afixed value for each physical layer.

The AIFS may be set to a value corresponding to the four types oftransmission queues mapped to the user priority levels.

The SIFS has the shortest time gap among the IFSs mentioned above.Accordingly, the SIFS may be used when an STA occupying a wirelessmedium needs to maintain the occupation of the medium without anyinterruption by another STA during a period in which a frame exchangesequence is performed.

That is, by using the shortest gap between transmissions within a frameexchange sequence, the STA may be assigned priority to complete anongoing frame exchange sequence. Also, the STA accessing the wirelessmedium by using the SIFS may immediately start transmission from theboundary of the SIFS without determining whether the medium is busy.

The duration of an SIFS for a specific physical (PHY) layer may bedefined based on a SIFSTime parameter. For example, the SIFS has a valueof 16 μs in physical (PHY) layers according to IEEE 802.11a, IEEE802.11g, IEEE 802.11n, and IEEE 802.11ac.

The PIFS may be used in order to provide an STA with the next highestpriority level after the SIFS. That is, the PIFS may be used to obtainpriority for accessing the wireless medium.

The DIFS may be used by an STA transmitting a data frame (MPDU) and amanagement frame (MAC protocol data unit (MPDU)) on the basis the DCF.After a received frame and backoff time expire, when it is determinedthat the medium is idle by a CS mechanism, the STA may transmit a frame.

FIG. 14 illustrates a frame transmission procedure in a WLAN system.

As described above, STAs 1410, 1420, 1430, 1440, and 1450 according tothis embodiment may individually select a backoff value for a backoffprocedure.

Each of the STAs 1410, 1420, 1430, 1440, and 1450 may attempt to performtransmission after waiting for time expressing the selected backoffvalue in slot time (i.e., the backoff window in FIG. 13).

Further, each of the STAs 1410, 1420, 1430, 1440, and 1450 may countdown the backoff window by slot time. The countdown for channel accessfor a wireless medium may be individually performed by each STA.

Hereinafter, a time corresponding to the backoff window may be referredto as a random backoff time (Tb[i]). That is, each STA may individuallyset a backoff time (Tb[i]) in a random backoff counter for each STA.

Specifically, the random backoff time (Tb[i]) corresponds to apseudo-random integer value and may be calculated by Equation 1 below.Tb[i]=Random(i)*SlotTime

Random(i) in Equation 1 denotes a function using uniform distributionand generating a random integer between 0 and CW[i]. CW[i] may beconstrued as a contention window that is selected between a minimumcontention window (CWmin[i]) and a maximum contention window (CWmax[i]).The minimum contention window (CWmin[i]) and the maximum contentionwindow (CWmax[i]) may correspond to CWmin[AC] and CWmax[AC], whichdefault values in Table 2.

In initial channel access, the STA may select a random integer between 0and CWmin[i], with CW[i] set to CWmin[i]. In this embodiment, theselected random integer may be referred to as a backoff value.

i may be understood as the user priority level of traffic data. That is,i in Equation 1 may be understood as corresponding to any one of AC_VO,AC_VI, AC_BE, and AC_BK in Table 1.

SlotTime in Equation 1 may be used to provide sufficient time for apreamble of the transmitting STA to be fully detected by a neighboringSTA. SlotTime in Equation 1 may be used to define the PIFS and the DIFSmentioned above. For example, SlotTime may be 9 μs.

For example, when the user priority level (i) is 7, an initial backofftime (Tb[AC_VO]) for a transmission queue of the AC_VO type may be timeexpressing a backoff value, which is selected between 0 andCWmin[AC_VO], in slot time.

When a collision occurs between STAs according to the backoff procedure(or when an ACK frame of a transmitted frame is not received), the STAmay calculate increased backoff time (Tb[i]′) by Equation 2 below.CWnew[i]=((CWold[i]+1)*PF)−1

Referring to Equation 2, a new contention window (CW_(new)[i]) may becalculated based on a previous contention window (CW_(old)[i]). PF inEquation 2 may be calculated in accordance with a procedure defined inIEEE 802.11e. For example, PF in Equation 2 may be set to 2.

In this embodiment, the increased backoff time (Tb[i]′) may be construedas time expressing a random integer (i.e., backoff value), which isselected between 0 and the new contention window (CW_(new)[i]), in slottime.

CWmin[i], CWmax[i], AIFS[i], and PF values mentioned in FIG. 14 may besignaled from an AP through a QoS parameter set element, which is amanagement frame. The CWmin[i], CWmax[i], AIFS[i], and PF values may bevalues preset by the AP and the STA.

Referring to FIG. 14, the horizontal axis (t1 to t5) for first to fifthSTAs 1410 to 1450 may indicate a time axis. The vertical axis for thefirst to fifth STAs 1410 to 1450 may indicate backoff time.

Referring to FIG. 13 and FIG. 14, if a particular medium is changed froman occupied or busy state to an idle state, the plurality of STAs mayattempt to transmit data (or a frame).

Here, to minimize a collision between STAs, each STA may select backofftime (Tb[i]) according to Equation 1 and may attempt transmission afterwaiting for slot time corresponding to the selected backoff time.

When a backoff procedure is initiated, each STA may count downindividually selected backoff counter time by slot times. Each STA maycontinuously monitor the medium while performing the countdown.

When the wireless medium is determined to be occupied, the STAs maysuspend the countdown and may wait. When the wireless medium isdetermined to be idle, the STAs may resume the countdown.

Referring to FIG. 14, when a frame for the third STA 1430 reaches theMAC layer of the third STA 1430, the third STA 1430 may determinewhether the medium is idle during a DIFS. When it is determined that themedium is idle during the DIFS, the third STA 1430 may transmit theframe to the AP (not shown). Here, although FIG. 14 shows the DIFS as aninterframe space (IFS), it should be note that this specification willnot be limited thereto.

While the frame is transmitted from the third STA 1430, the remainingSTAs may check the occupancy state of the medium and may wait for thetransmission period of the frame. A frame may reach the MAC layer ofeach of the first STA 1410, the second STA 1420, and the fifth STA 1450.When it is determined that the medium is idle, each STA may wait for theDIFS and may then count down backoff time individually selected by eachSTA.

FIG. 14 shows that the second STA 1420 selects the shortest backoff timeand the first STA 1410 selects the longest backoff time. FIG. 14 showsthat the remaining backoff time for the fifth STA 1450 is shorter thanthe remaining backoff time for the first STA 1410 at the time (T1) whena backoff procedure for the backoff time selected by the second STA 1420is completed and the transmission of a frame starts.

When the medium is occupied by the second STA 1420, the first STA 1410and the fifth STA 1450 may suspend the backoff procedure and may wait.When the second STA 1420 finishes occupying the medium (i.e., when themedium returns to be idle), the first STA 1410 and the fifth STA 1450may wait for the DIFS.

Subsequently, the first STA 1410 and the fifth STA 1450 may resume thebackoff procedure based on the suspended remaining backoff time. In thiscase, since the remaining backoff time for the fifth STA 1450 is shorterthan the remaining backoff time for the first STA 1410, the fifth STA1450 may complete the backoff procedure before the first STA 1410.

Referring to FIG. 14, when the medium is occupied by the second STA1420, a frame for the fourth STA 1440 may reach the MAC layer of thefourth STA 1440. When the medium is idle, the fourth STA 1440 may waitfor the DIFS. Subsequently, the fourth STA 1440 may count down thebackoff time selected by the fourth STA 1440.

Referring to FIG. 14, the remaining backoff time for the fifth STA 1450may coincidently match the remaining backoff time for the fourth STA1440. In this case, a collision may occur between the fourth STA 1440and the fifth STA 1450. If the collision occurs between the STAs, boththe fourth STA 1440 and the fifth STA 1450 may not receive an ACK andmay fail to transmit data.

Accordingly, the fourth STA 1440 and the fifth STA 1450 may individuallycalculate a new contention window (CW_(new)[i]) according to Equation 2.Subsequently, the fourth STA 1440 and the fifth STA 1450 mayindividually count down backoff time newly calculated according toEquation 2.

When then medium is occupied state due to transmission by the fourth STA1440 and the fifth STA 1450, the first STA 1410 may wait. Subsequently,when the medium is idle, the first STA 1410 may wait for the DIFS andmay then resume backoff counting. After the remaining backoff time forthe first STA 1410 elapses, the first STA 1410 may transmit a frame.

The CSMA/CA mechanism may include virtual carrier sensing in addition tophysical carrier sensing in which an AP and/or STA directly senses amedium.

Virtual carrier sensing is used to address any problem that may occur inaccess to a medium, such as a hidden node problem. For virtual carriersensing, the MAC of a WLAN system uses a network allocation vector(NAV). The NAV is a value representing remaining time for a medium to beavailable, which is indicated by an AP and/or STA currently using themedium or having the right to use the medium to another AP and/or STA.

Therefore, a value set as the NAV corresponds to a period in which an APand/or STA transmitting a frame is scheduled to use a medium, and an STAreceiving the NAV value is prohibited from accessing the medium duringthe period. The NAV may be set, for example, according to the value of aduration field in an MAC header.

The NAV may be understood as a timer for protecting the TXOP of atransmitting STA (e.g., a TXOP holder). A STA may not perform channelaccess in a period during which an NAV set for the STA is value, therebyprotecting the TXOP of a different STA.

FIG. 15 illustrates an example of setting an NAV.

Referring to FIG. 15, a source STA transmits an RTS frame, and adestination STA transmits a CTS frame. As described above, thedestination STA designated as a receiver through the RTS frame does notset an NAV. Some other STAs may receive the RTS frame to set up an NAV,and some other STAs may receive the CTS frame to set up an NAV.

If the CTS frame (e.g., a PHY-RXSTART.indication primitive) is notreceived within a certain period from when the RTS frame is received(e.g., when a MAC receives a PHY-RXEND.indication primitivecorresponding to the RTS frame), the STAs setting or updating the NAVthrough the RTS frame may reset the NAV (e.g., to 0). The certain periodmay be (2*aSIFSTime+CTS_Time+aRxPHYStartDelay+2*aSlotTime), whereCTS_Time may be calculated based on the length of the CTS frameindicated by the RTS frame and a data rate.

Although FIG. 15 shows that an NAV is set or updated through an RTSframe or a CTS frame for convenience, NAV setting/resetting/updating maybe performed based on a duration field of various other frames, such asa non-HT PPDU, an HT PPDU, a VHT PPDU, or an HE PPDU, (e.g., a durationfield in a MAC header of a MAC frame). For example, a STA mayset/reset/update an NAV if an RA field in a received MAC frame does notmatch an address (e.g., MAC address) of the STA.

Hereinafter, a technique for controlling uplink communication of an STAaccording to the present specification is described. The presentspecification proposes a technique for controlling an uplink accessmethod of a STA in a WLAN system. For example, uplink access may becontention-based uplink access. For example, an example ofcontention-based uplink access may be enhanced distributed channelaccess (EDCA) illustrated in FIG. 12 to FIG. 14.

In the present specification, a STA may use at least two techniques foruplink communication. For example, a first technique based on a triggerframe from an AP and a second technique based on contention describedabove may be used. Specifically, according to the first technique, theSTA may receive a trigger frame triggering UL MU communication from theAP and may configure a trigger-based (TB) PPDU based on uplink resourceinformation included in the trigger frame, thereby performing uplinkcommunication. Further, according to the second technique, the STA mayaccess a medium based on EDCA, thereby performing uplink communication.The STA according to the present specification may perform uplinkcommunication only through the first and second techniques during aspecific period set through a beacon or the like. Alternatively, the STAaccording to the present specification may perform uplink communicationthrough an additional technique in addition to the first/secondtechnique.

The conventional IEEE 802.11ax standard proposes a technique forincreasing UL MU gain by proposing a MU EDCA parameter. For example, atechnique for reducing the EDCA access probability of a STA by an APsetting a relatively large MU EDCA parameter is proposed. Specifically,the IEEE 802.11ax standard defines a new MU EDCA parameter in additionto a legacy EDCA parameter and proposes a technique enabling a STAcapable of UL MU to perform EDCA based on the MU EDCA parameter insteadof the legacy EDCA parameter.

However, in some cases, it is not preferable for a STA to perform EDCA.That is, in some cases, it is very difficult for the STA transmit uplinkdata based on EDCA. For example, when the STA exists at the edge of theBSS, it may be preferable for the STA to transmit uplink data through ULMU instead of EDCA due to a problem about transmission power of the STA.That is, it may be preferable for the STA to transmit a TB PPDU based ona trigger frame.

When the STA performs uplink communication through the TB PPDU, the STAcan perform uplink communication with a relatively small bandwidth ascompared with EDCA, thus successfully performing uplink communicationwith limited transmission power. For example, when uplink data istransmitted through EDCA, a 20-MHz band (or 20*N MHz) is needed fortransmission. However, when a TB PPDU is used, transmission with anarrow band, such as 26-RU or 52-RU, is possible, thus being favorablefor the STA positioned at the boundary of the BSS.

Accordingly, the present specification proposes a newoperation/mode/state of disabling/suspending/inactivating/prohibiting anEDCA operation of a STA. For convenience of description, when an EDCAoperation/connection of a STA isdisabled/suspended/inactivated/prohibited, it may be expressed that anEDCA-disabling operation is performed/applied. Accordingly, when anEDCA-disabling operation is performed/applied, the STA cannot perform anEDCA operation (i.e., EDCA-based medium access) until the EDCA operationis resumed, and thus the STA may perform uplink communication through ULMU (i.e., a TB PPDU). In some cases, when an EDCA-disabling operation isperformed/applied to a specific STA, the STA may perform uplinkcommunication only through UL MU (i.e., a TB PPDU).

EDCA-Disabling Condition

Hereinafter, a condition in which an EDCA-disabling operation isperformed/applied (i.e., an EDCA-disabling condition) is described.Illustrative EDCA-disabling conditions are as follows. That is, an EDCAoperation/connection of a STA may bedisabled/suspended/inactivated/prohibited based on the followingconditions. The following conditions may be used individually, ordifferent conditions thereof may be used at the same time.

Condition 1: Threshold Values of Downlink Received Signal StrengthIndication (DL RSSI) and/or DL Signal-To-Noise Ratio (SNR)

When the threshold values of a DL RSSI and/or a DL SNR of a downlink arenot satisfied, the EDCA-disabling operation may be performed. Forexample, when a value smaller than the threshold value is measured, theEDCA-disabling operation of the STA may be performed.

Condition 2: Threshold Value of Uplink (UL) Power Headroom

When the threshold value of UL power headroom is not satisfied, theEDCA-disabling operation may be performed. For example, a trigger framemay include the threshold value of UL power headroom of a TB PPDU. Whena UL power headroom value obtained for the STA is smaller than the valueincluded in the trigger frame, the EDCA-disabling operation of the STAmay be performed.

Condition 3: Threshold Value of Number of Failed SU Transmissions

When the number of failed SU transmissions of the STA exceeds athreshold value, the EDCA-disabling operation may be performed. Forexample, condition 3 may be information about the number of successivelyfailed SU transmissions.

Condition 4: Contention Window Size Among MU EDCA Parameters

The EDCA-disabling operation may be performed depending on whether acontention window for the STA reaches the maximum value. For example,when the contention window for the STA reaches the maximum value (e.g.,1024), the EDCA-disabling operation of the STA may be performed. Thecontention window reaching the maximum value indicates a very congestedstate. Therefore, when EDCA is performed with the contention windowreaching the maximum value, the channel state may worsen. Accordingly,the EDCA-disabling operation may be performed based on the contentionwindow for the STA.

The EDCA-disabling conditions may be transmitted to the STA by variousmethods. For example, information about the EDCA-disabling conditionsmay be transmitted from an AP through an association response/beacon, arecently received trigger frame, various other MAC frames, or othervarious PHY preambles. Alternatively, the EDCA-disabling conditions mayalready be stored in the STA.

EDCA-Disabling Operation

An EDCA-disabling operation of a STA may be performed in various ways.For example, the STA may directly determine whether to disable an EDCAoperation. Alternatively, an AP may determine whether to disable EDCA.Various embodiments of the EDCA-disabling operation are illustratedbelow.

Hereinafter, an example in which a STA directly determines whether todisable an EDCA operation is proposed.

First, when an EDCA operation of a STA is disabled, the STA may havefewer opportunities for UL access (i.e., a fairness problem) than otherSTAs. Therefore, the STA according to the present specification maydetermine whether to disable the EDCA operation and may then transmitinformation about the determination (i.e., information about thedetermination result) to an AP. That is, when the STA disables the EDCAoperation, the STA may transmit information about EDCA disabling (i.e.,information indicating EDCA disabling) through a UL frame.

Upon receiving the information about EDCA disabling, the AP mayconfigure a trigger frame based on the information. That is, the AP maydetermine the position and/or size of a UL RU (i.e., a UL RU used for aTB PPDU) included in the trigger frame based on the information aboutEDCA disabling. For example, the AP may allocate only an RU having afirst size or smaller (e.g., a 26-RU or a 52-RU) in a trigger framesubsequently transmitted for the EDCA-disabled STA. The first size maybe determined by various methods. For example, the STA may report inadvance information about the first size (e.g., a 26-RU or a 52-RU)through various MAC frames or MAC header information. That is, the STAmay provide recommendation information about the first size in advance.Through the foregoing operation, the fairness problem may be reduced.

FIG. 16 is a procedure flowchart illustrating an example of anEDCA-disabling operation according to the present specification. Some ofillustrated steps may be omitted, and the order of the steps may bechanged. The example illustrated FIG. 16 relates to an example in whicha STA directly determines whether to disable an EDCA operation.

In S1610, a STA may receive/obtain control information about anEDCA-disabling operation. For example, the STA may receive at least oneparameter (e.g., a DL RSSI illustrated above) related to anEDCA-disabling condition for the STA in S1610.

The STA may determine whether to disable an EDCA operation of the STAbased on the control information received/obtained in S1610 (S1620). Forexample, the STA may determine whether the EDCA-disabling condition issatisfied, and may choose/determine to disable the EDCA operation of theSTA based on the determination.

When the STA determines to disable EDCA, the STA may immediately applythe EDCA-disabling operation before transmitting an additional signal toan AP. In this case, S1630 or S1640 may be omitted.

Additionally or alternatively, the STA may transmit the result ofdetermination in S1620 to the AP (S1630), and may apply theEDCA-disabling operation after receiving additional control informationfrom the AP (S1640). For example, S1630 may be a request to disableEDCA, and S1640 may be a response to S1630. The response to S1640 mayinclude information about acceptance or rejection.

For example, S1630 may be performed through a general UL frame (e.g., aUL PPDU including a flag field in a legacy or new field of a MACheader). In addition, S1640 may be performed based on an immediateresponse corresponding to the UL frame in S1630. For example, theinformation in S1640 may be received through an ACK or block ACK (BA)frame for the UL frame in S1630. Alternatively, the information in S1640may be received through a separate DL frame.

When S1630 is a request to disable EDCA, the AP may accept or reject therequest based on various pieces of information. For example, the AP maydetermine whether to accept/reject the request based on the size of aresource for UL MU at the time when S1630 is performed. That is, the APmay reject the request in S1630 when the size of the resource for UL MUis a threshold value or smaller.

S1610 and/or S1620 may be repeatedly performed. For example, when theEDCA-disabling condition is updated, the AP may further perform S1610.Alternatively, even though the EDCA-disabling condition is not updated,S1610 may be repeatedly performed in a preset time interval.

The STA may repeatedly determine whether the EDCA-disabling condition issatisfied based on an EDCA-disabling condition alreadyreceived/obtained. For example, after the EDCA-disabling condition issatisfied, when the STA determines that the EDCA-disabling condition isno longer satisfied (S1620), the STA may resume the EDCA operation ofthe STA. Resumption of an EDCA operation may be expressed ascontinuation of participation in an EDCA operation.

The EDCA operation may be resumed immediately after S1620 or may beresumed after S1640. That is, the STA may immediately resume the EDCAoperation without request/permission to resume the EDCA operation.Alternatively, the STA may transmit information about the resumption ofthe EDCA operation to the AP (e.g., transmit a UL PPDU including a flagfield in a legacy or new field of a MAC header) in S1630 and may receiveinformation about acceptance or rejection of the resumption of the EDCAoperation in S1640.

A condition for resuming the EDCA operation may be the same as theabove-described EDCA-disabling conditions or may be defined separately.That is, a threshold value for disabling EDCA and a threshold value forresuming EDCA may be defined separately.

According to the foregoing details, the STA may perform the followingoperations. The STA may calculate whether the target RSSI of the AP canbe satisfied when transmitting a SU PPDU based on the target RSSI of theAP, the size of a scheduled RU, a MCS, AP TX power, and STA powerheadroom information included in a recently received trigger frame. Whenthere is TX power headroom information while satisfying the target RSSI,the STA determines to be able to perform SU transmission and may resumeEDCA. That is, the STA may obtain an EDCA-disabling condition (or acondition for resuming the EDCA operation) (S1610) and may determinewhether to disable or resume EDCA based on the condition (S1620).

As described above, S1630 may be performed through frames in variousformats. For example, the STA may include information about EDCAdisabling by inserting a one-bit flag into a legacy OM control field.

FIG. 17 illustrates an example of an OM control field for S1630. Asillustrated, an EDCA access disable bit may be included in the OMcontrol field and may indicate information about EDCA disabling (e.g.,information about the result of determination in S1620).

FIG. 18 is a procedure flowchart illustrating another example of anEDCA-disabling operation according to the present specification. Some ofillustrated steps may be omitted, and the order of the steps may bechanged. The example illustrated FIG. 18 relates to an example in whichan AP determines whether to disable an EDCA operation of a STA.

In S1810, an AP may determine whether to disable an EDCA operation of aSTA based on control information about an EDCA-disabling operation(i.e., the foregoing EDCA-disabling condition). For example, when the APtransmits a trigger frame and receives an HE TB PPDU from the STA beforeS1810, the AP may determine whether to disable or enable EDCA of the STAusing TX power headroom information and RSSI information transmitted bythe STA. The EDCA-disabling condition used in S1810 may be the same asthe condition used in S1610.

The AP may instruct/command the STA to disable EDCA based on S1810(S1820). S1820 may be performed based on various DL frames (e.g., a DLPPDU including a flag field in a legacy or new field of a MAC header).

After receiving the instruction/command to disable EDCA in S1820, theSTA may immediately disable the EDCA operation of the STA (S1830).

In S1830, the STA may not immediately apply an EDCA-disabling operation.For example, the STA may determine whether to accept or reject theinstruction/command from the AP in S1830. Here, the STA may determinewhether to accept or reject the indication/command from the AP inconsideration of the size and priority level of buffered traffic storedin a UL buffer, UL power headroom, and DL and/or UL channel states.

In S1840, the STA may transmit information about the result ofdetermination in S1830 to the AP. That is, information about whether theSTA accepts or rejects the instruction/command from the AP may betransmitted in S1840. S1840 may be performed through various types of ULframes (e.g., a UL PPDU including a flag field in a legacy or new fieldof a MAC header). For example, S1840 may be performed through the OMcontrol field illustrated in FIG. 17.

When the STA accepts the instruction/command from the AP, theEDCA-disabling operation may be applied immediately after S1840. Whenthe STA rejects the instruction/command from the AP, the STA may accessa medium based on the EDCA operation.

Similarly to the example of FIG. 16, the steps of FIG. 18 may berepeatedly performed. For example, when the EDCA-disabling condition isupdated as in the example of FIG. 16, steps from S1810 may be performedagain. Further, when the AP determines that the EDCA-disabling conditionis no longer satisfied in S1810 as in the example of FIG. 16, the APgives an instruction/command to resume EDCA. The instruction/command toresume EDCA may be performed in S1820.

In this specification, the AP or the STA may determine whether todisable the EDCA operation of the STA. For example, a mode in which theSTA determines EDCA disabling may be referred to as a firstdetermination mode, and a mode in which the AP determines EDCA disablingmay be referred to as a second determination mode. That is, the firstdetermination mode is related to the example of FIG. 16, and the seconddetermination mode is related to the example of FIG. 18.

The STA and the AP may selectively use the first/second determinationmodes. For example, a particular STA may support only one determinationmode or all the determination modes. In addition, a particular AP maysupport only one determination mode or all the determination modes. TheSTA and the AP may negotiate capability information about adetermination mode through an association process described withreference to FIG. 2. Subsequently, the STA and the AP may selectivelyuse the first determination mode or the second determination mode basedon a negotiated determination mode.

The examples of the present specification may be further modified below.

As described above, the EDCA operation of the STA may bedisabled/suspended/inactivated/prohibited according to the determinationof the STA or the AP. When an EDCA operation of a particular STA isdisabled through various examples of FIG. 16 and FIG. 18, it ispreferable that the AP frequently allocates an uplink RU (i.e., a UL MUresources used for a TB PPDU) through a trigger frame. For example, itmay be preferable that the AP allocates a narrow bandwidth (e.g., a26-RU or a 52-RU) through a trigger frame for a STA having an EDCAoperation disabled and more frequently allocates an RU resource to theSTA. For this operation, it is important for the STA to be allocatedmore buffer status report (BSR) resources. That is, since the AP candetermine a UL MU resource based on a BSR from the STA, it is preferableto allocate more BSR resources to the STA having EDCA disabled (i.e.,the EDCA-disabled STA).

The STA may transmit a BSR based on UL OFDMA random access (UORA)defined according to the IEEE 802.11ax standard.

FIG. 19 illustrates a method of performing UORA in a WLAN system.

As illustrated in FIG. 19, an AP may allocate six RU resources through atrigger frame (e.g., illustrated in FIG. 9 to FIG. 11). Specifically,the AP may allocate a first RU resource (AID 0, RU 1), a second RUresource (AID 0, RU 2), a third RU resource (AID 0, RU 3), a fourth RUresource (AID 2045, RU 4), a fifth RU resource (AID 2045, RU 5), and asixth RU resource (AID 2045, RU 6). Information about AID 0 or AID 2045may be included, for example, in the user identifier field 1110 of FIG.11. Information about RU 1 to RU 6 may be included, for example, in theRU allocation field 1120 of FIG. 11. AID=0 may indicate a UORA resourcefor an associated STA, and AID=2045 may indicate a UORA resource for anunassociated STA. Accordingly, the first to third RU resources of FIG.19 may be used as UORA resources for an associated STA, and the fourthand fifth RU resources of FIG. 19 may be used as UORA resources for anunassociated STA. The sixth RU resource of FIG. 19 may be used as aresource for general UL MU.

In the example of FIG. 19, as an OFDMA random access backoff (OBO)counter for STA1 is decreased to 0, STA1 randomly selects the second RUresource (AID 0, RU 2). In addition, since an OBO counter for STA2/3 isgreater than 0, no uplink resource is allocated to STA2/3. Further, inFIG. 19, since the AID (i.e., AID=3) of STA4 is included in the triggerframe, STA4 is allocated a resource of RU 6 without backoff.

Specifically, since STA1 of FIG. 19 is an associated STA, there are atotal of three eligible RA RUs (RU 1, RU 2, and RU 3) for STA1, andaccordingly STA1 decreases the OBO counter by 3 to 0. Since STA2 of FIG.19 is an associated STA, there are a total of three eligible RA RUs (RU1, RU 2, and RU 3) for STA2, and accordingly STA2 decreases the OBOcounter by 3 but the OBO counter is greater than 0. Since STA3 of FIG.19 is an unassociated STA, there are a total of two eligible RA RUs (RU4 and RU 5) for STA3, and accordingly STA3 decreases the OBO counter by2 but the OBO counter is greater than 0.

Referring to the example of FIG. 19, a legacy trigger frame indicateswhether a particular random RU resource (i.e., a UORA RU) is allocatedfor an associated STA or for an unassociated STA. However, the legacytrigger frame does not include information about whether the particularrandom RU resource is for an STA performing an EDCA-disabling operation.

The present specification proposes an example of improving the legacytrigger frame. That is, as described above, it is preferable toguarantee an opportunity to use a random RU resource for a STA having anEDCA operation disabled. To this end, an AP may allocate a random RUresource that is available only for an EDCA-disabled STA.

A method of allocating a random RU resource for an EDCA-disabled STA maybe determined variously.

First Example

As described above, when the user identifier field 1110 of FIG. 11 isset to a first value (i.e., 0), the subsequent RU allocation field 1120may be used for a random RU resource for an associated STA; when theuser identifier field 1110 of FIG. 11 is set to a second value (i.e.,2045), the subsequent RU allocation field 1120 may be used for a randomRU resource for an unassociated STA. This specification proposes usingthe RU allocation field 1120 for a random RU resource for anEDCA-disabled STA when the user identifier field 1110 of FIG. 11 is setto a third value (e.g., 2044).

In this case, random RU resources (UORA RUs) may be classified intothree types. That is, random resources (i.e., eligible RA RUs) used todecrease an OBO counter for a STA may be classified into three types.Specifically, the total number of RU allocation fields 1120 subsequentto a user identifier field 1110 set to the first value (i.e., AID=0) inone trigger frame may be used to decrease an OBO counter for anassociated STA. Further, the total number of RU allocation fields 1120subsequent to a user identifier field 1110 set to the second value(i.e., AID=2045) in one trigger frame may be used to decrease an OBOcounter for an unassociated STA. In addition, the total number of RUallocation fields 1120 subsequent to a user identifier field 1110 set tothe third value (i.e., AID=2044) in one trigger frame may be used todecrease an OBO counter for an EDCA-disabled STA.

The first example may be variously modified.

In the first example, EDCA-disabled STAs may use not only an RUallocation field (i.e., an RU allocated in a trigger frame set toAID=2044) subsequent to a user identifier field set to the third value(e.g., 2044) but also an RU allocation field (i.e., an RU allocated in atrigger frame set to AID=0 or AID=2045) subsequent to a user identifierfield set to the first or second value (e.g., 0 or 2045) according tothe connection state thereof.

For example, EDCA-disabled STAs related to an AP may perform a UORAprocedure using both RUs allocated in a trigger frame with an AID set to2044 and RUs allocated in a trigger frame with an AID set to 0.Unassociated EDCA-disabled STAs may perform a UORA procedure using bothRUs allocated in a trigger frame with an AID set to 2044 and RUsallocated in a trigger frame with an AID set to 2045.

Second Example

This specification proposes an additional example of allocating a randomRU resource for an EDCA-disabled STA.

FIG. 20 illustrates an example of additional information included in auser info field of a trigger frame. That is, FIG. 20 illustrates anexample of control information included in the user info field (e.g.,960 #1 to 906 #N of FIG. 9) of the trigger frame. Specifically, a fieldillustrated in FIG. 20 is information included in the user info field ofthe trigger frame when the user identifier field 1110 of FIG. 11 is setto 0 or 2045. More specifically, a number of RA-RU field of FIG. 20indicates the number of consecutive RUs allocated for UORA. For example,the value of the number of RA-RU field of FIG. 20 may be the number ofconsecutive RUs minus 1. A more RA-RU field of FIG. 20 may includeinformation about whether a random RU resource is allocated in a nexttrigger frame.

This specification proposes an additional example of allocating a randomRU resource for an EDCA-disabled STA by changing the fields of FIG. 20.

FIG. 21 illustrates an example of control information according to anexample of the present specification.

As illustrated in FIG. 21, when a newly proposed restricted RA RU fieldis set to a specific value (e.g., 1), random RUs allocated by a userinfo field (e.g., 960 #1 to 906 #N in FIG. 9) of a trigger frame may beused only for an ECDA-disabled STA.

A method of determining a random resource (i.e., an eligible RA RU) usedto decrease an OBO counter for a STA in the second example may be thesame as that illustrated in the first example.

The second example may be variously modified.

In the second example, when the restricted RA RU field is set to aspecific value (e.g., 1), EDCA-disabled STAs using the allocated randomRUs may be restricted by an AID value. For example, when the AID is thefirst value (e.g., 0), only associated EDCA-disabled STAs use theallocated random RUs; when the AID is the second value (e.g., 2045),only unassociated EDCA-disabled STAs use the allocated random RUs.Alternatively, the associated EDCA-disabled STAs may perform a UORAoperation using not only random RUs allocated in a trigger frame havingan AID of the first value (e.g., 0) and a restricted RA RU field set toa specific value (e.g., 1) but also random RUs allocated in a triggerframe having an AID of the first value (e.g., 0) and a restricted RA RUfield set to 0, and the unassociated EDCA-disabled STAs may perform aUORA operation using not only random RUs allocated in a trigger framehaving an AID of 2045 and a restricted RA RU field set to a specificvalue (e.g., 1) but also random RUs allocated in a trigger frame havingan AID of 2045 and a restricted RA RU field set to 0.

FIG. 22 illustrates an operation according to a modified example of thepresent specification.

For example, in S2210, it may be determined whether to apply anEDCA-disabling operation to a STA. S2210 may be performed through all orsome of S1610 to S1640 of FIG. 16 or may be performed through all orsome of S1810 to S1840 of FIG. 18.

In S2220, the STA may receive a trigger frame including a random RUresource only for an EDCA-disabled STA from an AP. The first example orthe second example described above may be used as a method for includingthe random RU resource only for the EDCA-disabled STA.

In S2230, the STA may perform a random backoff operation based on thereceived trigger frame. When the random RU resource only for theEDCA-disabled STA is included according to the foregoing first/secondexample, the STA may perform the backoff operation by reducing an OBOcounter by the number of random RU resources included in the receivedtrigger frame (the number of random RU resources only for theEDCA-disabled STA). When the OBO counter is 0, the STA may configure aTB PPDU based on one of the random RU resources only for theEDCA-disabled STA. In this case, BSR information about the STA may beincluded in the TB PPDU.

In S2240, the STA may transmit the TB PPDU through a selected resource.The STA may transmit the TB PPDU through the RU resource determinedthrough S2230.

FIG. 23 illustrates an example of a PPDU to which an example of thepresent specification is applied.

The examples illustrated above in FIG. 16/FIG. 18/FIG. 22 may beperformed based on a PPDU illustrated in FIG. 23. That is, each step maybe performed through a PPDU according to an EHT standard (or differentWLAN standard). The PPDU illustrated in FIG. 23 may include features ofsome of the foregoing HE-PPDU formats.

All or some of illustrated parts (i.e., fields) may be divided into aplurality of subparts/subfields. Each field (and subfields thereof) maybe transmitted in a unit of 4 us*N (N is an integer). Further, eachfield may include a guard interval (or short GI) according to aconventional Wi-Fi standard. A common subcarrier frequency spacing value(delta_f=312.5 kHz/N or 312.5 kHz*N, N=integer) may be applied to all ofthe illustrated fields, or first delta_f may be applied to a first part(e.g., the entirety of a legacy part and the entirety/part of a SIGpart) and second delta_f (e.g., smaller than first delta_f) may beapplied to the entirety/part of the remaining part.

Some of the illustrated fields may be omitted, and the order of thefields is for illustration and may thus be changed in various ways. Forexample, a subfield (e.g., EHT-SIG-A and/or HARQ-SIG) of an EHT SIG part2320 may be disposed before an EHT STF part 2330, and a remainingsubfield (e.g., EHT-SIG-B/C or HARQ-SIG) of the EHT SIG part 2320 may bedisposed after the EHT STF part 2330.

A legacy part 2310 of FIG. 23 may include at least one of a non-HT shorttraining field (L-STF), a non-HT long training field (L-LTF), and anon-HT signal field (L-SIG). The EHT SIG part 2320 of FIG. 23 mayinclude various pieces of control information for a PPDU to betransmitted. For example, the EHT SIG part 2320 may include controlinformation for decoding the EHT STF part 2330, an EHT LTF part 2340,and data 2350. For example, HE-SIG-A information described above may beincluded in an EHT-SIG-A field, and HE-SIG-B information described abovemay be included in an EHT-SIG-B field. The EHT STF part 2330 of FIG. 23may include a training field (i.e., an STF sequence). The STF sequencepresented in this specification may reduce a PAPR. In addition, the STFsequence may help a receiving STA in configuring an AGC gain through arepeated pattern. The EHT LTF part 2340 of FIG. 23 may include atraining field (i.e., an LTF sequence) for channel estimation.

The data field 2350 of FIG. 23 may include an MPDU or AMPDU. Theaforementioned OM control field of FIG. 17 may be included in a MACheader of the data field of FIG. 23, and information about EDCAdisabling disclosed in FIG. 16/FIG. 18/FIG. 22 may be included in thedata field of FIG. 23.

FIG. 24 illustrates an example of a STA to which an example of thepresent specification is applied.

Referring to FIG. 24, the STA 2400 may include a processor 2410, amemory 2420, and a transceiver 2430. Characteristics of FIG. 24 may beapplied to a non-AP or an AP STA. The processor, the memory, and thetransceiver may be configured as separate chips, or at least twoblocks/functions may be configured through one chip.

The transceiver 2430 transmits and receives a signal. Specifically, thetransceiver 2430 may transmit and receive an IEEE 802.11 packet (e.g.,IEEE 802.11a/b/g/n/ac/ax/be packets and the like).

The processor 2410 may implement the functions, processes, and/ormethods proposed herein. Specifically, the processor 2410 may receive asignal through the transceiver 2430, may process a reception signal, maygenerate a transmission signal, and may perform control for signaltransmission.

The processor 2410 may include an application-specific integratedcircuit (ASIC), a separate chipset, a logic circuit, and a dataprocessor. The memory 2420 may include a read-only memory (ROM), arandom access memory (RAM), a flash memory, a memory card, a storagemedium, and/or other storage devices.

The memory 2420 may store a signal received through the transceiver(i.e., a reception signal) and a signal to be transmitted through thetransceiver (i.e., a transmission signal). That is, the processor 2410may obtain a received signal through the memory 2420 and may store asignal to be transmitted in the memory 2420.

FIG. 25 is a block diagram specifically illustrating a transceiver. Someor all blocks illustrated in FIG. 25 may be included in the processor2410. Referring to FIG. 25, the transceiver 110 includes a transmitter111 and a receiver 112. The transmitter 111 includes a discrete Fouriertransform (DFT) unit 1111, a subcarrier mapper 1112, an IFFT unit 1113,a CP inserter 1114, a radio transmitter 1115. The transmitter 111 mayfurther include a modulator. Also, for example, the transmitter 111 mayfurther include a scramble unit (not shown), a modulation mapper (notshown), a layer mapper (not shown), and a layer permutator (not shown),and these elements may be positioned before the DFT unit 1111. That is,in order to prevent an increase in the peak-to-average power ratio(PAPR), the transmitter 111 allows information to pass through the DFTunit 1111 before mapping a signal to a subcarrier. After performingsubcarrier mapping of a signal, which is spread (or precoded, in thesame sense) by the DFT unit 1111, through the subcarrier mapper 1112,the signal passes through the inverse fast Fourier transform (IFFT) unit1113 into a signal on a time axis.

The DFT unit 1111 performs DFT on inputted symbols, thereby outputtingcomplex-valued symbols. For example, when Ntx symbols are inputted(where Ntx is a natural number), a DFT size is equal to Ntx. The DFTunit 1111 may also be referred to as a transform precoder. Thesubcarrier mapper 1112 maps the complex-valued symbols to eachsubcarrier in the frequency domain. The complex-valued symbols may bemapped to resource elements corresponding to a resource block beingassigned for data transmission. The subcarrier mapper 1112 may also bereferred to as a resource element mapper. The IFFT unit 1113 performsIFFT on the inputted symbols, thereby outputting a baseband signal fordata, which corresponds to a time-domain signal. The CP inserter 1114duplicates an end part of the baseband signal for the data and insertsthe duplicated part to a front part of the baseband signal for the data.By performing CP insertion, inter-symbol interference (ISI) andinter-carrier interference (ICI) may be prevented, thereby allowingorthogonality to be maintained even in a multi-path channel.

The receiver 112 includes a radio receiver 1121, a CP remover 1122, anFFT unit 1123, and an equalizer 1124. The radio receiver 1121, the CPremover 1122, and the FFT unit 1123 of the receiver 112 respectivelyperform the inverse functions of the radio transmitter 1115, the CPinserter 1114, and the IFFT unit 1113 of the transmitter 111. Thereceiver 112 may further include a demodulator.

The transceiver of FIG. 25 may include a reception window controller(not shown) to extract part of a reception signal and a decodingprocessor (not shown) to decode a signal extracted through a receptionwindow in addition to the illustrated blocks.

What is claimed is:
 1. A method for a wireless local area network (WLAN)system, the method comprising: receiving, by a station (STA) from anaccess point (AP), a downlink (DL) physical protocol data unit (PPDU)including first control information related to a received signalstrength indication (RSSI) threshold; determining, by the STA, whetherto disable an enhanced distributed channel access (EDCA) operation ofthe STA based on the first control information; and transmitting, by theSTA to the AP, an uplink (UL) PPDU including an operating mode (OM)control field, wherein the OM control field includes: a first sub-fieldhaving a length of 3 bits related to a number of reception (RX) spatialstreams (SSs) of the STA, a second sub-field having a length of 2 bitsrelated to a channel bandwidth of the STA, a third sub-field having alength of 1 bit related to whether to disable an uplink multi-user (ULMU) transmission of the STA, a fourth sub-field having a length of 3bits related to a number of transmission (TX) SSs of the STA, a fifthsub-field having a length of 1 bit related to whether to disable anextended range single-user (ER SU) transmission of the STA, and a sixthsub-field having a length of 1 bit related to disabling the EDCAoperation of the STA, wherein the first sub-field is contiguous to thesecond sub-field being contiguous to the third sub-field beingcontiguous to the fourth sub-field being contiguous to the fifthsub-field being contiguous to the sixth sub-field; and receiving, by theSTA from the AP, a trigger frame soliciting a trigger-based (TB) PPDUtransmission of the STA, wherein the trigger frame includes allocationinformation related to a resource unit (RU) allocated to the STA,wherein the RU has a size of 26 sub-carriers or 52 sub-carriers.
 2. Themethod of claim 1, wherein the first control information furtherincludes: a threshold value of a downlink received signal strengthindication (DL RSSI), a threshold value of a DL signal-to-noise ratio(SNR), and/or a threshold value of an uplink (UL) power headroom for theSTA.
 3. The method of claim 1, wherein the OM control field is includedin a MAC protocol data unit (MPDU) of the UL PPDU transmitted to the AP.4. A station (STA) in a wireless local area network (WLAN) system, theSTA comprising: a memory to store a transmission signal and a receptionsignal; and a processor connected to the memory, wherein the processoris configured to: receive, from an access point (AP), a downlink (DL)physical protocol data unit (PPDU) including first control informationrelated to a received signal strength indication (RSSI) threshold;determine whether to disable an enhanced distributed channel access(EDCA) operation of the STA based on the first control information; andtransmit, to the AP, an uplink (UL) PPDU including an operating mode(OM) control field, wherein the OM control field includes: a firstsub-field having a length of 3 bits related to a number of reception(RX) spatial streams (SSs) of the STA, a second sub-field having alength of 2 bits related to a channel bandwidth of the STA, a thirdsub-field having a length of 1 bit related to whether to disable anuplink multi-user (UL MU) transmission of the STA, a fourth sub-fieldhaving a length of 3 bits related to a number of transmission (TX) SSsof the STA, a fifth sub-field having a length of 1 bit related towhether to disable an extended range single-user (ER SU) transmission ofthe STA, and a sixth sub-field having a length of 1 bit related todisabling the EDCA operation of the STA, wherein the first sub-field iscontiguous to the second sub-field being contiguous to the thirdsub-field being contiguous to the fourth sub-field being contiguous tothe fifth sub-field being contiguous to the sixth sub-field; andreceiving, from the AP, a trigger frame soliciting a trigger-based (TB)PPDU transmission of the STA, wherein the trigger frame includesallocation information related to a resource unit (RU) allocated to theSTA, wherein the RU has a size of 26 sub-carriers or 52 sub-carriers. 5.The STA of claim 4, wherein the first control information furtherincludes: a threshold value of a downlink received signal strengthindication (DL RSSI), a threshold value of a DL signal-to-noise ratio(SNR), and/or a threshold value of an uplink (UL) power headroom for theSTA.
 6. The STA of claim 4, wherein the OM control field is included ina MAC protocol data unit (MPDU) of the UL PPDU transmitted to the AP.